Over the past six months, a massive campaign has revved up to get COVID-19 vaccines into the arms of people across the globe. Doctors initially rolled out the immunizations to older people and those with underlying health problems. Now, as teens roll up their sleeves — and younger kids prepare to do so — some have started asking a big question: Will we all need booster vaccines?
“No one knows” if booster shots will be needed, says Kirsten Lyke. She’s an expert in vaccine science. She works at the University of Maryland School of Medicine in Baltimore. But if boosters are needed, it shouldn’t be too surprising. People need a new shot in the arm every year to fend off influenza.
SARS-CoV-2 is the virus that causes COVID-19. As with the flu virus, the new coronavirus has been mutating. Newly emerging variants respond to the original vaccines. But there’s concern those variants will eventually get around the immunity that our bodies developed to the first versions of the vaccine. And that may mean boosters are needed.
The good news: More than half of U.S. residents have gotten at least one dose of a COVID-19 vaccine. As a result, U.S. cases and deaths have plunged to their lowest levels since March 2020.
Here’s what we know so far about the possible need for booster shots.
Immunity lasts at least six months
Whether and when people might need a booster shot rests largely on how long the body’s immune system protects against us becoming very ill. For COVID-19, this protection lasts at least six months, researchers say. It could possibly last much longer. Data on this have been emerging from people who were infected last year.
Once the virus gains a toehold, the body unleashes a wave of immune troops to fight it off. They include antibodies and so-called T cells. Antibodies typically attack the virus itself. T cells raise additional alarm bells or kill infected cells. Together, antibodies and T cells defeat the virus and then help the immune system form a memory of the virus, explains Ali Ellebedy. He’s an immunologist. He works at Washington University School of Medicine in St. Louis.
That immune memory is crucial. It turns on the whole protection cycle again if and when someone gets exposed to the virus once more.
So far, Ellebedy says, immune memory to SARS-CoV-2 has largely been following the rules — at least for most people.
Nearly everybody has been developing an immune memory to the coronavirus, studies are finding. Some antibody-producing cells continue to work long after the virus has left the body. That should protect people who encounter SARS-CoV-2 again. Ellebedy found signs of these cells in people who had recovered from COVID-19. Those with even mild symptoms had antibody-producing immune cells in their bone marrow 11 months after infection. Ellebedy was part of a team that reported this May 24 in Nature.
Growing evidence now suggests that vaccines offer similar — if not better — protection. If true, boosters might not be needed for some time. Right now, things look “pretty good,” Lyke says. People who got the Moderna vaccine still had high levels of antibodies six months after getting their second dose. Researchers shared the finding in April. And a jab of Pfizer’s vaccine remained 91.3 percent effective against COVID-19 symptoms after six months. Pfizer shared this in an April 1 news release.
Still, “we don’t know how any of these COVID-19 vaccines perform past the one-year mark,” Lyke says. Scientists are keeping a close eye on them, though.
The role of coronavirus variants
Available vaccines still protect people from the worst of COVID-19. But that might not always be true. COVID-19 vaccines already show signs they can be less effective against some new variants.
If it weren’t for the variants, “I don’t think we would be talking about potentially boosting,” says Ellebedy. “What we are seeing so far is that the vaccine is really robust. So why would we even need a booster if the virus doesn’t change?”
Companies are already testing booster shots to fight some variants. Some tests have focused on the so-called beta variant. It first emerged in South Africa. Early results from Moderna, for instance, hint that people who receive its booster shot against a viral protein in the beta variant develop antibodies to that variant. The antibodies sparked by this booster were better at stopping the variant from infecting lab-grown cells than were ones from people who got a third dose of the original vaccine.
For now, no one knows what the best variant booster might look like, says Jerome Kim. He’s a vaccine scientist and director-general of the International Vaccine Institute. Its headquarters is in Seoul, South Korea.
Mix and match for vaccines?
To prepare for a future where people might need COVID-19 boosters, the U.S. National Institute of Allergy and Infectious Diseases launched a clinical trial on June 1. It will test the value of mixing and matching COVID-19 vaccines.
The big question is whether this approach will strengthen the immune response, says Lyke. She’s a researcher leading the trial. These scientists want to know what will happen if someone is given an mRNA vaccine — such as Moderna’s or Pfizer’s — and then is given a different type as a booster (such as Johnson & Johnson’s vaccine). “Can we increase [the immune response]?” Lyke asks.
It’s not a crazy idea. Mixing different types of Ebola vaccines or HIV vaccines, for example, can trigger stronger immune responses than getting multiple doses of the same vaccine. The idea is that a second type of shot will activate some extra part of the immune system, Lyke explains. That way, she hopes, “You get the best of both.”
Early results from a similar trial being conducted in the United Kingdom hint that the answer for COVID-19 shots is yes.